Education Journalist | Study Abroad Strategy Lead
Thallus refers to the vegetative tissue of some organisms in which these tissues are not organized into organs. Thalli do not have organized parts such as leaves, roots, stems, branches as well as vascular bundles. This type of structure is mainly found in the plant body of algae, fungi and other lower organisms which commonly belongs to a group known as Thallophyte. Cell plates and filaments are the main compositions of the thallus. Thallophytes usually don’t grow from the apical point of the body. The organism whose body structure is undifferentiated or resembles a thallus is commonly called thalloid, thalloid, thalli form, ethaline or thallus. The unique characteristic of the thallophytes is that they consume glucose as soon as it is produced in photosynthesis.
| Table of Contents |
Key Terms: Thallus, Plasmodium, Motile, Daughter Cells, Xylem
What is Thallus?
[Click Here for Sample Questions]
Thallus refers to the vegetative structure that is not differentiated into distinct parts of a plant such as leaves, stems, branches, vascular bundles, etc. It is made up of cell plates and filaments. It ranges from unicellular structure to complex structure.
Thallus
Structural Organization of Thallus in Algae
[Click Here for Previous Year Questions]
Thallus does have different structures. Algae show the presence of cell walls however few don’t have cell walls. They may have branched or unbranched filaments. The different structures of Thallus are as follows.
-
Unicellular type
Except for Phaeophyceae, all algae groups have a unicellular type of thallus. They are characterized by the presence of flagella. They may have one or more flagella, usually two or in multiples of two. They may have a rigid cell wall. In some forms, the outer layer of the protoplast gives a definite shape to the cell or may cause a change in shape (amoeboid forms). They are further divided into the following categories….
- Unicellular Amoeboid forms or Rhizopodial forms
- Unicellular motile (Flagellated) forms
- Unicellular Non- motile (Protococcoidae) forms
-
Aggregates
When thallus is formed by the collection of many single cells, it is known as aggregates that do not have a fixed number of cell shapes or sizes. They form mas like aggregation in a gelatinous structure. During cell division, the daughter cells don’t leave the gelatinous mass which leads to an increase in cell number in the same gelatinous mass. Aggregates are further subdivided into:
- Palmelloid Habit
- Dendroid Forms
- Rhizopodial Forms
Range of Thallus Structure in Algae
-
Colonial forms
Colonial aggregation is formed when the unicellular forms are connected with each other by a Cytoplasmic thread. They form colonies in a mucilaginous covering. Colonial forms are observed in Chlorophyceae, Bacillariophyceae, Chrysophyceae, Dinophyceae, Xanthophyceae, etc.
They are further divided into.
- Motile Colonial forms
- Non – motile Colonial forms
-
Filamentous forms
It resembles a knit structure. In this form, a single cell is divided into many daughter cells with septa between them. The common lateral walls are derived from the mother cell. Filamentous forms are further classified as:
- Un- branched filaments
- Branched filaments
Branched filaments are further classified as:
- Branched Simple
- Heterotrichous
- Pseudoparenchymatous forms
-
Siphonaceous forms
When the plant body grows without cross-wall formation except during reproductive organs formation. It leads to the formation of a tube-like structure or coenocyte.
-
Parenchymatous forms
When a cell divides in more than one plane, filamentous habit gets modified into a thallus. This is known as the parenchymatous form. This thallus may be in the form of a leaf-like or foliose structure.
Also Read:
Structural description of Thallus in Fungi
[Click Here for Sample Questions]
The different structures of Thallus in Fungi are as follows:
1. Unicellular Thallus
In lower fungi, unicellular Thallus is present which are spheric in structure. This Thallus plays a significant role in the reproduction of lower fungi. If the Thallus is present in unicellular and holocarpic form (reproductive cell is formed from the whole Thallus), the mycelium of the Thallus will be absent. Plasmodium and yeast are also characterized by the presence of unicellular Thallus.
2. Filamentous Thallus
Filamentous Thallus develops when the germination of the spore takes place. During germination, the spore gets to the substratum where all the conditions to sustain life are favourable. The tubular structure develops from spores which further become filamentous. The Thallus remains in this structure which is known as hyphae. Reproductive organs of fungi are developed from these hypha filaments in an advanced stage. This fungus is known as eucarpic fungi.
Thallus
Function of Thallus
Thallus serves as the reproductive organs for fungi and other lower organisms. It makes the organism reproduce by both sexual or asexual means. It also helps in the formation of colonies in Fungi.
Read more : Gametophyte
Types of Thallus
[Click Here for Previous Year Questions]
The two types are:
1. Homothallism
When a single organism has the ability to reproduce sexually, it is known as homothallism. In homothallic special, both male and female structures are present in the same organism. An individual spore can produce a sexually reproducing colony while propagated in isolation. It usually takes place in lower fungi different cells of single mycelium perform opposite sexual functions.
2. Heterothallism
When two compatible partners take part in reproduction, it is known as heterothallism. A zygote is formed by the contribution of different individuals. Common examples are saccharomyces cerevisiae, Aspergillus fumigated, Aspergillus flavus, Penicillium Menefee and Neurospora crassa.
Types of Thallus
Habitat
Thallophytes are usually present in aquatic habitats. They may also be present in other places too such as moist stone, soil and wood. Since they are present in those places where there is a presence of water, xylem is not necessarily required. Hence they are devoid of xylem.
Read Also : Fungus Life Cycle
Reproduction in Thallus
[Click Here for Sample Questions]
Reproduction in Thallus takes place by the following methods.
-
Vegetative method
Thallus type structure is usually divided by the process of fragmentation. In this method, each fragment is capable of producing a new organism.
-
Asexual method
It takes place by zoospores which may be motile or non-motile. If motile, they are flagellated. These spores further germinate into a plant when they come in contact with the appropriate condition.
-
Sexual method
Sexual reproduction takes place by the fusion of two gametes from different individuals. It is further divided into the following three types.
-
Isogamous type
When fused gametes are similar in structure, it is known as the Isogamous type. Gametes may be motile or non-motile. They are morphologic logically the same but physiologically different.
-
Anisogamous type
When gametes are morphologically the same but with different sizes, they are of the Anisogamous type. The larger gamete is called macrogamete and the smaller one is microgamete.
-
Oogamous type
When fusion takes place between female gamete which is large, non-motile, food-laden and non-flagellated with motile male gamete. This type of fusion is known as Oogamous type fusion.
Read Also : Sexual Reproduction in Flowering Plants
Nutrition
Thallophytes such as algae have different colour pigments for carrying out photosynthesis such as chlorophyll, xanthoph, carotenoids etc. Algae and fungi often show symbiotic association with each other. They mostly flourish in aquatic, damp or moist environments.
Also Read:
Things to remember
- Thallus is an undifferentiated tissue that is not organised into distinct organs.
- They range from unicellular to multicellular forms.
- They are mostly found in aquatic or damp environments.
- They exhibit a vegetative, asexual and sexual mode of reproduction.
- Glucose is consumed immediately after its production by thallophytes. The remaining glucose is stored as starch.
- Members of the thallophyte group are autotrophic in the case of algae. However, fungi are heterotrophic in nature.
- Sexual reproduction takes place by the fusion of two gametes.
- The cell wall of algae is made up of cellulose whereas the cell wall of fungi is made up of chitin.
Read more : Sexual Reproduction in Fungi
Previous Year Questions
- The integument of Cycas ovule is hard on account of…? [COMEDK UGET 2005]
- Vascular plants which produce seeds but not fruits belong to the group…? [COMEDK UGET 2009]
- Pteridophytes are also called…? [COMEDK UGET 2005]
- Which one of the following is not a character of Bryophytes? [COMEDK UGET 2006]
- Sex organs in pteridophytes are…? [CUCET 2012]
- Which of the following is not present is thallus of Marchantia? [CUCET 2012]
- Carpogonium is formed in…? [CUCET 2012]
- Syngamy is the fusion of…? [CUCET 2012]
- Mitospores of algae are differentiated by…? [CUCET 2012]
- Fucoxanthin is characteristic pigment of…? [CUCET 2012]
- Which one among the following groups of plants is placed in the beginning of…? [COMEDK UGET 2011]
- Among the following which structure is not functionally similar to others…? [COMEDK UGET 2011]
- Smooth and pegged rhizoids are present in the gametophytes of….? [COMEDK UGET 2010]
- Prothallus is…? [BCECE 2013]
- Reserve food material of algae is…? [BCECE 2006]
- Cycas belongs to gymnosperms due to…? [BCECE 2006]
- In Bryophyta, a specialized organ of the sporophyte for attachment to the gametophyte…? [UPSEE 2017]
- In Pinus, male cone bears a large number of…? [BCECE 2016]
- Coralloid root is the feature of…? [BHU UET 2008]
- 'Club moss' belongs to…? [BHU UET 2006]
Sample Questions
Ques. What are the components of Thallus? (3 marks)
Ans. The Thallus is mainly made up of cell plates and filaments and ranges from unicellular to multicellular forms. It is present in all the lower fungi and algae (unicellular as well as multicellular). In algae, different pigments are also present for carrying out photosynthesis. The structure of Thallus is very simple and does not show distinct structures such as stems leaves, flowers, etc. They also lack vascular bundles such as xylem and phloem.
Ques. What is achlorophyllous thallophytes? (3 marks)
Ans. The thallophytes which are devoid of chlorophyll is known as achlorophyllous thallophytes.
- They are heterotrophic in nature and completely depends on autotrophs for their food.
- They have differentiated bodies that include a mass of cells known as thallus.
- They also grow in moist and damp places. Moisture is an important factor for their growth.
- Fungi also form a symbiotic relationship with algae. Algae provide nutrition to fungi through photosynthesis. In return, Fungi absorbs moisture and nutrients for algae. This symbiotic association between algae and fungi is known as lichens.
Ques. What do you mean by Holocarpic and Eucarpic Thallus? (5 marks)
Ans. Holocarpic and Eucarpic Thallus are parts of fungi.The characteristics of Holocarpic Fungi are as follows:
- Holocarpic Thallus
- When the entire Thallus gets converted into a reproductive structure such as sporangium on maturation, then this type of fungi is known as the holocarpic fungi.
- This type of fungi is characterized by the conversion of the entire Thallus into a reproductive cell.
- Examples are Synchytrium endobioticum, chytridiomycota.
- Eucarpic Thallus
- In Eucarpic Thallus, the Thallus gets converted into vegetative as well as reproductive structures.
- In this case, the substratum is attached to the reproductive cell.
- Most of the fungi are examples of Eucarpic Thallus.
Ques. What is the importance of fungi in Medicine? (5 marks)
Ans. Fungi is an important part of medicine in the following ways-
- Fungi are used to make antibiotics to kill pathogens. Actinomycetes and moulds produce antibiotics that inhibit the growth of certain pathogens.
- They are also used to make penicillin which has no effect on humans but it can kill gram-positive bacteria.
- Streptomycin is also made by fungi that have the ability to kill gram-negative bacteria.
- Ergot is used to control bleeding post-childbirth. It is also used in certain medicines and vet clinics.
- Stomach cancer can be prevented by consuming clavatia fungi.
- Lysergic acid is used in the field of psychiatry. It is a derivative of ergot.
- Griseofulvin is used in the treatment of fungal infections.
Ques. Why algae and fungi are classified as Thallophytes? (5 marks)
Ans. Algae and Fungi are classified as Thallophytes because of the following reasons –
- Their body is not differentiated into distinct organs such as stem, branches, leaves, etc. They look like a mass of cells (Thallus).
- They do not have vascular bundles such as xylem and phloem for the conduction of water and minerals. Therefore, both are found in those places which have moist, wet or aquatic conditions.
- Both algae and fungi exhibit asexual as well as a sexual mode of reproduction. Sexual reproduction takes place by the formation and fusion of two gametes.
- Both algae and fungi don’t show growth from their apical points.
- Although both have Thalloid structures, they show major differences. Algae perform photosynthesis due to the presence of chlorophyll while fungi are dependent on autotrophs.
Ques. What is the economic importance of fungi? (5 marks)
Ans. Fungi is very important for human beings in the following ways –
- Medicines- Fungi is used to produce a number of medicines to cure several disorders. It includes penicillin, Lysergic acid, Streptomycin, ergot, Griseofulvin, etc.
- Food Industry– Mushrooms are consumed directly as food. Fungi are also used in the food processing industry. Fungi are widely used in the baking and brewing industries. Saccharomyces cerevisiae is an important ingredient for bread. They also carry out photosynthesis.
- Agriculture- Fungi can increase plant growth by about 70%. They are involved in the formation of humus and thereby increasing the fertility of the soil.
- Biological insecticides and pesticides– Several fungi can kill several insects without affecting plants. Examples – Empausa sepulchralis, Cordyceps melonhae, Beauveria bassiana, etc.
- Reusing– They decompose dead and decaying plant and animal matter and hence enrich the soil with hummus. They increase soil fertility. They help in preventing the formation of debris and thereby is beneficial to the environment.
Ques. What is the economic importance of thallophytes? (5 marks)
Ans. Thallophytes are economically important in a variety of ways. They are used as:
- Food: Algae and fungi are an important source of nutrients and is often used in many food items. It is rich in carbohydrates, fats, proteins and vitamins. It also contains many minerals such as iron, potassium, zinc, etc. They are also used in the preparation of various medicines and are often used as supplements.
- Fodder: Algae are also used as fodder to feed cattle. Rhodymenia palmate is used to feed livestock such as cattle and chickens in many countries.
- Pisciculture: Algae are also used in fish farming. Fishes like to feed on Blue-green and green algae. It is also used to absorb carbon dioxide from the environment and at the same time to provide oxygen to the water.
- Fertilizers- Red and brown algae are used as fertilizers. Seaweed extract is also used to produce liquid fertilizers.
- Binding agent: Algae are also used to bind the soil. Hence, they are useful to prevent soil from erosion.
- Food products: Algae are used to produce many food products. They can be used as addictive or used in the thickening of food. They are also used in many household products such as toothpaste.
Do Check Out:
Comments